Global warming threatens cold-water fish, scientists say

Extinction could be the result for some cold-water fish species as temperatures rise and habitats shrink. (Photo: Wikimedia)
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Brooks Hays

The human species has adapted to all sorts of climates and habitats, populating the far reaches of the globe. Humans, of course, can get up and move to avoid the consequences of rising temperatures, or apply and shed layers of clothing as the weather demands. Fish — a species humans are intensely reliant on as a food source — aren’t quite as nimble.

According to a recent study in Nature, scientists say many species of cold-water fish have already been affected by rising global ocean temperatures and may be among the first major casualties of climate change.

Global fisheries have been reacting to the earth's rising temperatures over the last four decades, with warming waters attracting new temperate and tropical species, while cold-water species are forced to search for chillier locales. This may be good for fishermen in Nova Scotia hoping to catch Spanish mackerel, but it’s bad for lox lovers. “For salmon and many other species, there is a narrow temperature range that they can live in due to limitations in body function,” William Cheung, co-author of the study and researcher on the University of British Columbia, recently told the Vancouver Sun. “Warm water causes them to suffer poor growth and reproduction and they may die from the heat stress.”

Scientists in the U.K. say sea bass and red mullet are showing up in unusually large numbers in British waters, while more traditional species of the North Sea, like cod, are migrating northward as temperatures rise.

Pacific salmon are for the first time being caught in Beaufort Sea, the body of water off the northern coast of Alaska. The Inuit there, who are catching them, apparently have no name for the new species.

But while salt-water fish are more or less free to migrate, chasing ideal temperatures and environmental conditions into new bodies of water and readapting to new sea level depths, fish which have persisted for decades in freshwater streams, rivers, ponds, and lakes may not be so lucky.

A recent study by the National Wildlife Federation (NWF) says global warming is proving detrimental to a variety of freshwater species, including smallmouth bass and trout. Rising temperatures are shrinking suitable habitat for cold-water species like trout and landlocked salmon, the study contends. Brook trout, for example, are missing from more than a third of their original habitat up and down the East Coast. Higher temperatures also encourage disease and allow invasive species to move into new territories and compete for food.

But global warming’s byproducts – the consequences of higher temperatures – may serve as the biggest threat to fish, researchers and conservationists at NWF suggest. Reduced rainfall, longer droughts, shorter winters, and less snow all translate to lower, slower stream flows, making life more difficult for already vulnerable and struggling species. Wildfires, on the rise as hotter, drier weather persists, are also to blame, as tree loss means less shade for riverbanks and the water’s edges — where fish often feed and escape the heat — and less protection from contaminants that wash into the river when it rains.

These findings have resulted in increased calls from environmentalists and conservationists for the government to strengthen protections for endangered species and depleted commercial fishing stocks, reduce fossil fuel use, and bolster pollution regulations.

And it’s not just fish that stand to suffer. Recreational fishing is a $26 billion industry in the U.S. Meanwhile, commercial fishing operations in the U.S. generate some $4 billion a year in revenues. And -- for the time being at least -- a lot of food for hungry homo sapiens.

The federal government has acknowledged the realities of climate change and its impacts on fish and other species. Last year, several federal agencies partnered in developing and publishing the National Fish, Wildlife and Plants Climate Adaptation Strategy, a plan to "enable natural resource administrators, elected officials, and other decision makers to take action to adapt to a changing climate." Agencies, including the Fish and Wildlife Service and the National Oceanic and Atmospheric Association, said federal policies must do better to mitigate non-climate wildlife stressors, such as "habitat loss, fragmentation, and degradation, invasive species, disease, pollution, overharvesting, [and] destructive harvest practices," for species to have a better chance of adapting to a warmer climate.